The volume of oil and brine inside cased wells varies greatly. It is often desirable for oil producers to survey and measure the volume and depth of the oil column in any given cased oil well. It is well known that water is heavier than oil (oil floats on water) and brine is heavier than water due to the specific gravity of each medium. xe2x80x9cSpecific gravityxe2x80x9d is the ratio of mass of a,solid or liquid to the mass of an equal volume of distilled water at 4xc2x0 C.). The specific gravities of water, oil and brine are well known to those skilled in the art. Water has a specific gravity of 1.0 g/cc. Oil has a specific gravity less than water ranging between 0.7 and 0.95 g/cc, and oil brine has a specific gravity of greater than water approximately, 1.3 g/cc. Consequently, the oil column always sits atop the brine column in any cased oil column. The principle problem in surveying the oil column and measuring the volume of oil in a cased oil well is in distinguishing between the oil and brine and at what depth the oil stops and the brine begins.
Heretofore, sophisticated electronic equipment have been used to survey and measure the oil in the static fluid columns of cased oil wells. Conventional surveying equipment uses the difference in electrical capacitance between the oil and brine to survey the fluid column in the oil well. The conventional electronic surveying equipment includes an instrument pack and sensor probe connected to the instrument pack by a long length of electrical wiring. The instrument pack sends an electrical signal to the probe and monitors the change in capacitance sensed by the probe at different depths in the well. The corrosive environment within the fluid column of an oil well is hard on the delicate electrical sensors of the probe. Most importantly, this type of surveying equipment is expensive, complicated and impractical for frequently monitoring multiple oil wells. A simple and inexpensive alternative is desirable.
The surveying instrument of this invention and its method of use utilizes the inherent differences in specific gravity between water, oil and brine, rather than the difference in electrical capacitance to provide a more simple, convenient, portable and cost effective means for surveying and measuring the volume of oil and brine in the static fluid columns of cased oil wells. The instrument includes a probe, and a modified fishing rig used to lower and raise the probe into the oil well. The fishing rig includes a handled rod, a reel with a numeric line counter, and a length of fused braided, non-stretch fishing line. The numeric line counter visually indicates the length of line expelled from the reel""s spool. The probe includes a tubular casing, which is filled with ordinary tap water. The probe is constructed and filled with water so that it has a specific gravity greater than oil and less than brine (approximately 1.0 g/cc).
The instrument is used by simply lowering the probe down the oil well and monitoring its rate of descent via the line counter. The probe will descent rapidly through the air zone of the well. Once the probe reaches the top of the oil column and enters the oil, the probe will continue to descend down the well because of oil""s higher specific gravity, but at a noticeably slower rate. Once the change in the rate is detected, the operator records a depth reading from the counter, which marks the depth of the top of the oil column. The probe will stop at the top of the brine column, because the specific gravity of the brine is greater than that of the probe. Once the probe stops, the operator records a second depth reading from the counter, which marks the bottom of the oil column and the top of the brine column. The difference between the first and second readings provides the height of the oil column. From the height of the oil column and the diameter of the well bore, the volume of oil in the column can be easily calculated. If the well depth is known, the volume of the brine column can also be extrapolated.
Accordingly, an advantage of the instrument of this invention and its method of operation is that it utilizes the inherent differences in specific gravity between water, oil and brine to provide a more simple, convenient, portable and cost effective means for surveying and measuring the volume of oil and brine in the static fluid columns of cased oil wells.
Another advantage of this invention is that the instrument eliminates the complex and delicate electrical circuitry of conventional electronic surveying equipment.
Another advantage of this invention is that the instrument is durable and reused, whereas, the delicate electrical sensor probes of conventional equipment must be painstakingly maintained and frequently replaced.
Another advantage of this invention is that the instrument is inexpensive, compact and portable.
Another advantage of this invention is that the instrument can be used by operators with relatively little training and sophistication.
Another advantage of this invention is that a single operator uses the instrument to survey multiple wells in an oil field in a relatively short amount of time and at a fraction of the cost of using conventional electronic equipment.
Other advantages will become apparent upon a reading of the following description.